Technical Field
The present invention relates to shovels and methods of controlling a shovel.
Description of Related Art
In shovels, a boom, an arm, and a bucket are generally driven by respective hydraulic cylinders. Hydraulic oil supplied to the hydraulic cylinders or hydraulic oil discharged from the hydraulic cylinders is controlled by a control valve. Furthermore, the opening and closing of valves in the control valve is controlled by a pilot hydraulic system different from a drive hydraulic system.
For example, a pilot pressure for controlling the driving of a boom cylinder for driving the boom is controlled by a boom operation lever to be supplied to the control valve. That is, a pilot pressure commensurate with the amount of operation of the boom operation lever is supplied to the control valve. The control valve opens or closes in accordance with this pilot pressure to allow hydraulic oil to be supplied to the boom cylinder or allow hydraulic oil to be discharged from the boom cylinder.
Here, for example, consideration is given to the case where an operator of the shovel operates the boom operation lever during turning to raise and thereafter stop the boom. In this case, first, a pilot pressure commensurate with the amount of operation of the boom operation lever is supplied to the control valve, so that the control valve is controlled to allow high-pressure hydraulic oil to be supplied to the bottom side of the boom cylinder. As a result, the boom rises. When the operator returns the boom operation lever to a neutral position to stop the boom, the pilot pressure becomes substantially zero, so that the control valve closes to stop hydraulic oil from being supplied to the bottom side of the boom cylinder. Usually, the operator returns the boom operation lever to a neutral position in a rapid action. Therefore, the pilot pressure as well rapidly decreases to become a value close to zero.
When the boom rises and thereafter rapidly decelerates to stop as in the above-described case, the hydraulic pressure in the boom cylinder changes because of the rapid deceleration of the boom. This change of the hydraulic pressure changes the hydraulic pressure at the hydraulic supply port of a turning hydraulic motor as well, so that the turning body of the shovel swings in the turning direction. Such swinging of the vehicle body of the shovel is unpleasant to the operator.